In the conventional art, the technology of portable power tools such as electric drills, power hammers, electric saws, electric wrenches, etc., is generally mature. A typical portable power tool comprises a casing, a motor, a gear train, and a power head driven by the motor via the gear train.
To keep a portable power tool compact and for maximum force, there is a constant demand to reduce the size of the motor and to increase the output power.
Hence there is a desire for a motor which has a high power density.